Heretofore, a technique for measuring the thickness of a thin film formed on a light-transmissive substrate by using optical absorption characteristics of a material has been known (for example, see Patent Document 1).
Patent Document 1 discloses a technique in which, in a production line of thin film solar cells, light is radiated to a substrate of a solar cell provided with a thin film, and the thickness thereof is obtained from the amount of light transmitted through the substrate.
Patent Document 1: Japanese Unexamined Patent Application Publication No. 2003-65727